1. Field of the Invention
The invention relates to a manufacturing method for a wheel rolling bearing device, and a wheel rolling bearing device.
2. Description of Related Art
A wheel rolling bearing device (so-called “wheel hub unit”) and a manufacturing method for the wheel rolling bearing device are described in, for example, Japanese Patent Application Publication No. 2006-111070 (JP 2006-111070 A) and Japanese Patent Application Publication No. 2007-268690 (JP 2007-268690 A). In a manufacturing method for an existing wheel rolling bearing device 101 shown in FIG. 7A, described in JP 2006-111070 A, a shaft member 106 (having a fitting shaft portion 109, flanges 107 and a shaft portion 105) for a wheel rolling bearing device is formed as a single-piece member through cold forging, and a hollow cylindrical portion 115 (indicated by the dotted line) that will be a clinched portion 117 used to fix an inner ring 142 is formed at one end of the shaft portion 105. Then, after the inner ring 142 is fitted to the cylindrical portion 115, the cylindrical portion 115 is clinched radially outward to form the clinched portion 117 to thereby fix the inner ring 142. In addition, in an existing wheel rolling bearing device 201 shown in FIG. 7B, described in JP 2007-268690 A, a hollow cylindrical portion 215 (indicated by the dotted line) that will be a clinched portion 217 used to fix an inner ring 242 is formed by turning at one end of a shaft member 206 for a wheel rolling bearing device. Then, after the inner ring 242 is fitted to the cylindrical portion 215, the cylindrical portion 215 is clinched radially outward to form the clinched portion 217 to thereby fix the inner ring 242.
In the related art described in JP 2006-111070 A, the cylindrical portion 115 to which the inner ring 142 is fitted is formed through cold forward extrusion, and a die needs to have a shape corresponding to the cylindrical portion. Therefore, the shape of the die is slightly complex. In addition, in the related art described in JP 2007-268690 A, the cylindrical portion 215 to which the inner ring 242 is fitted is formed through turning. Therefore, extra equipment, time and costs are required for turning. In addition, the clinched portion 117 (see FIG. 7A) in JP 2006-111070 A and the clinched portion 217 (see FIG. 7B) in JP 2007-268690 A each are formed by clinching the cylindrical portion. Therefore, the center portion of the clinched portion is hollow, and the stiffness of the clinched portion is low.